In the manufacture of dynamoelectric machines such as DC motors and generators, it is well known that necessary components thereof consist of a stationary magnetic circuit structure (often referred to as the "field"); a magnetic circuit structure that rotates relative to the field (often referred to as an "armature"); a frame or housing structure that supports the dynamoelectric machine; one or more bearings that support the armature shaft relative to the field so that relative rotation therebetween may be achieved; and electrical switching means (e.g., a commutator assembly and brushes) for selectively making electrical connections with electrical conductors (often called "windings") in the machine.
Commutation is performed so that magnetic fields or poles associated with the armature and field have desired instantaneous predetermined spatial relationships such that the desired dynamoelectric effect is achieved (i.e., the conversion of mechanical energy to electrical energy in the case of a generator, or the conversion of electrical energy to mechanical energy in the case of a motor). As will be understood in the case of a motor, the forces of magnetic attraction and repulsion cause the armature to rotate relative to the field and deliver useful output torque or mechanical energy to the output shaft.
DC motors of both the permanent magnet and the wound coil type are generally described in numerous references works or publications. One such publication is the book entitled "Fractional And Subfractional Horsepower Electric Motors" by Cyril G. Veinott and Joseph E. Martin, 4th Edition, published by the McGraw-Hill Book Company bearing a copyright notice of 1986 and further identified as ISBN 0-07-067393-4.
It will be understood by those skilled in the art that successful operation of a motor or generator is dependent upon continuous, normal performance of all of the components thereof that have been mentioned hereinabove. Thus, failure of a bearing, winding, or commutator all can have the same objectionable results, i.e., failure of the dynamoelectric machine to operate at worst, or degraded performance at best.
While the present invention (described in detail hereinbelow and claimed in the concluding portion of this specification) may be utilized in conjunction with either motors or generators, discussion from this point forward will be with reference only to motors or machines, and thus redundant reference to generators specifically or dynamoelectric machines generally will be avoided.
One of the modes of electrical failure associated with machines that utilize commutators has to do with insulation breakdown or failure, in the region of the in-board end of armature commutators. As will be understood, brushes which make electrical contact with commutators typically are formed of carbon and such brushes normally wear down during operation of the machine. This process results in degradation products (e.g., carbon dust) from such brush wear being present in increasingly large amounts during the life of a machine. Such dust is present within the interior of the machine and particularly within the vicinity of the commutator structure. Conductive materials such as carbon dust or powder, dirt, moisture, oil, and so forth result in electrical leakage paths and tracking currents that, with time, can build to sufficiently high levels to cause electrical failure of the machine.
It thus will be understood that it would be desirable to provide new and improved processes of manufacturing machines that utilize commutators, and to provide new and improved commutator and armature constructions that would better survive the accumulation of oil, water, moisture, and other contaminants.
It also would be desirable to provide such processes and products that could be reliably and economically manufactured; and that could contribute to increased life of the machine.
Accordingly, it is a general object of the present invention to provide new and improved methods of manufacturing dynamoelectric machines having improved insulating properties so that premature failure thereof, associated with electrical failure of a commutator, may be reduced, if not eliminated.
It is another object of the present invention to provide new and improved dynamoelectric machine designs having structural characteristics and component interrelationships that provide increased resistance to failure associated with commutator leakage currents.
It is a more specific object of the present invention to provide new and improved processes and product features of dynamoelectric machines such that commutator leakage currents do not lead to objectionable levels of deposits of tracking materials and tracking currents at levels sufficiently excessive to cause nuisance ground fault detection situations or premature electrical failure.
It is a more specific object to provide processes and product features for the general purpose described hereinabove, wherein improved insulation systems and processes providing the same result in structures that are fire resistant, so as to reduce the risk of burning interior machine components in event of flashover (i.e., violent arcing) from a commutator element to ground, or between positive and negative brushholders.
It is yet an even more specific object of the present invention to provide new and improved products and processes of making the same which will provide desirable insulating features and yet will also maintain sufficient mechanical and dimensional integrity to resist displacement and destruction of parts thereof due to centrifugal forces that are inherently associated with rotating masses.